Applications are known in which it is necessary to have a cooled and/or almost totally dry fluid, in both distribution plants and in user machines.
Among the most widespread known cooling plants there are those in which the fluid is cooled by means of a cooling circuit comprising at a heat exchanger, called evaporator, which by means of a direct or indirect heat exchange, has the function of cooling the fluid to be cooled to the desired temperature or, in drying plants for compressed air, to make the water present in the fluid condense due to cooling, and then allow to separate the water from the fluid by means of suitable separator devices, to subsequently discharge it through suitable discharge devices.
The cooling circuit of said plants generally consists of a cooling compressor, a condenser, a expansion member and said evaporator.
The condenser can be for example, but not only, of the static type, with a finned battery, a finned battery with forced cooling using an electroventilator, with a bundle of pipes with water cooling, or other.
The expansion member can be for example, but not only, an expansion valve, a capillary, a capacity regulation valve, a thermostatic valve, an electrovalve, or other.
These components are suitably sized so as to guarantee, to the nominal conditions of delivery, pressure and temperatures, an effective cooling of the fluid to a pre-established temperature.
In such known plants, to prevent the cooling conditions determined by the plant from becoming excessive or insufficient as the characteristic parameters of the fluid to be cooled vary, two different control techniques are mainly used. A first technique, typical of domestic refrigerators, provides to switch off the cooling unit until the correct conditions of refrigeration have been restored, and then restart the cooling unit when it reaches a pre-established threshold for re-starting refrigeration.
A second technique provides to install at least a device able to limit the cooling capacity, such as for example a capacity regulation valve or hot gas by-pass system, or a system to control the speed of rotation of the compressor, or others. The function of these devices is to choke the flow of cooling fluid in the event that a modification is detected in one or more significant parameters of the fluid to be cooled.
However, the two known techniques entail various difficulties in management and coordination, stress to the motors, and slow response times, while the second technique also implies high costs of production and maintenance.
It is also known to provide systems to measure the pressure/temperature of the cooling fluid circulating both at outlet from the condenser and also at outlet from the expansion member, associated with intervention means such as thermostats or pressure switches, the function of which is to keep the pressure values constant, inside a pre-determined range, in said two points of the circuit. In this way, however, apart from having to intervene in two points with problems of reciprocal coordination, in any case there is a delay both in the intervention and also in achieving the effects of the intervention.